Following in the footsteps of the Sun's smooth-talking and sagacious political editor, Trevor Kavanagh, is not perhaps the most enviable of prospects. In football terms it is a bit like succeeding Sir Alex Ferguson at Manchester United. Kavanagh has prowled the corridors of Westminster for more than two decades, representing Britain's best-selling red-top daily with gravitas and the sure diplomatic touch of a whiskered elder statesman. This week, his deputy, George Pascoe-Watson, 39, settles into the hot seat, acutely aware that he has one of the toughest acts on Fleet Street to emulate. Yet he shows little sign of being daunted by the task ahead of him.

When MediaGuardian confirmed nine months ago that Kavanagh would relinquish his post, it led to speculation about who would succeed him. But it now appears that Pascoe-Watson had been assured several years earlier that he would inherit the position. Indeed, in the eerily quiet late-morning surroundings of the bar at the Cinnamon Club, a favourite restaurant of the Westminster set, Pascoe-Watson has no hesitation in admitting that he had been painstakingly "groomed" for the job by Kavanagh himself. It appears a plan has long been in place for a seamless transition of power - perhaps in marked contrast to the story both men have so frequently written about, namely the fractious and protracted jostling between 10 and 11 Downing Street.

"For some years now getting the job was on the cards," he says, "and we've been talking about the future. But of course you never really know until it happens. Obviously it was always down to [the Sun's editor] Rebekah Wade who to choose in the end, but it was certainly Trevor who groomed me and put me up for the job." How involved was the Sun's proprietor Rupert Murdoch? Pascoe-Watson replies carefully: "It is a position that Mr Murdoch was advised about and discussed with [Kavanagh]. And he had to grant his permission. So this was very much an issue which went right to the top of the company."

Pascoe-Watson describes Kavanagh, who will stay in the lobby as the paper's associate editor writing commentary and columns, as his "mentor". In fact, so unflinchingly loyal is he, you get the feeling that, if it ever came down to it, he would take a bullet for the man he succeeds. "Trevor is unique," he says. "I have worked with him for 11 years, 10 as his deputy, and he has taught me the tricks of the trade. He taught me how to get information and how to treat information. He also taught me how to write. Not every journalist on newspapers can write and Trevor has a fantastic way of writing in language that is universally understandable. His copy is flawless and goes in untouched."

Like Murdoch, Kavanagh believes in "small government, low tax and strong defence". It comes as no surprise that Pascoe-Watson's own convictions mimic those of his mentor. "I have always had that approach to the world. It was drummed into me, I suppose, by my father. I don't care which colour wraps around the politics. What I care about is what is the right thing for the country and Sun readers. And it's always small state, strong defence, strong law and order, the freedom of the individual not to be nannied, the general view that human beings are best left to their own devices as far as possible and to give people the incentive to have a better life."

Which sounds like Thatcherism in all but name. Measured in manner and tone, with a clipped, posh Edinburgh voice, Pascoe-Watson, like Kavanagh, represents the acceptable, corporate face of the Sun. Less the foot-in-the-door hack wheedling for stories (though he is no doubt capable of that too), more the immaculately-turned-out operator, equally at home on Radio 4 and at Chequers, as on one of the paper's annual meet-the-readers jaunts to caravan parks and holiday camps.

Another thing he has picked up from Kavanagh is how to cope with "the responsibility that comes with the power of the paper" and its 10 million readers. He is, he says, all too aware of the clout he will wield as the paper's political editor and will try to use it "sparingly". Furthermore, he acknowledges that a battering by the Sun can snuff out political careers. "I am not the kind of person to go around saying I can finish off a cabinet minister because that's not in my nature. But it is certainly true that we can make life very difficult for politicians if in fact they have erred and they deserve to be removed from office in our view."

The post brings access too. He is discreet enough to deny that the big beasts of British politics have rung him in person to congratulate him, but he says "people around" Tony Blair, Gordon Brown and David Cameron have. Over the years, he has been a regular visitor to Downing Street for face-time with the PM as part of a contingent of Sun executives. Now he can expect a flood of invitations. He will also see more of Murdoch too.

But whether he will be seeing rather too much of Kavanagh, who will still be sitting just "two feet away" from him in the lobby, is a moot point. Is there a danger that his mentor's continuing presence will gradually evolve from a comfort blanket to a curse? "I have thought about that a lot," says Pascoe-Watson. "But I would never say it is a curse. Some people I dare say will be asking 'how can you be the new Trevor Kavanagh?' You can't. And once you accept that, you have to do the job as you see fit. I will do it in the way I have been taught to do it, but not with any sense of how can I get out of his shadow. Over time that will happen."

There was a moment when it seemed the Kavanagh succession plan might be disrupted. In the summer of 2004 the BBC attempted to entice Pascoe-Watson, an accomplished broadcaster, away from the Sun to join News 24 as political editor. "They were talking about trying to get me to take on Sky News. They said they'd build the channel around me. There were many sticking points, the most important of which was that I didn't particularly want to do it because I already by that stage had been told that I was going to get Trevor's job." In the end, the job went in-house, to James Landale.

Given that it might also have made for uncomfortable and possibly compromising pillow-talk with his partner, the Sky News anchor Kay Burley, Pascoe-Watson has no doubt that he made the right call. "Being in print in politics is 10,000 times better in every respect than being in broadcasting," he says. "Even for someone of [BBC political editor] Nick Robinson or [ITN political editor] Tom Bradby's level. They always have to be in places to do interviews and standups, they have to bother with packages and all the rest of it. Our job at the end of the day is to fish for information and the more time I can spend doing that the better."

Pascoe-Watson has plenty of experience at the journalistic coalface. Born in Edinburgh in 1966, the son of an RAF pilot and a nursing sister, he eschewed a university education and instead completed a two-year journalism diploma at Napier College in Edinburgh. (Napier only became a university later, in 1992.) Reporting jobs in the West Country followed, but when the news agency he worked for went bust, he packed all his belongings into his Ford Cortina and holed up in a cousin's squat in Tooting, south London. Having rung every newsdesk in the capital, he started shifting on the Sun the night of his arrival. He was 21, and has been there ever since.

Pascoe-Watson has reported on three administrations, two Tory and one Labour, and the big question is whether the Sun's always qualified but now fast-evaporating support for Tony Blair will vanish entirely as the prime minister prepares to leave Downing Street. The paper's backing for New Labour always centred on Blair, himself, rather than the party and there are certainly signs that the Sun is warming to David Cameron. Pascoe-Watson reveals that Murdoch, whose policy is to back winners, has held a meeting with Cameron in the past couple of months. In words that might chill the blood of Gordon Brown, he says: "We are very impressed by Cameron. I would say that at this time, there has never been a better time for the Sun to look more favourably at the Conservatives. We like what we see of him so far. The next four years give Cameron - and Brown - the opportunity to impress or let down the Sun."

Cameron's appeal, it turns out, is that he is, like Blair, a pretty straight sort of guy. Despite the upper crust trappings, Citizen Dave appears to be, according to the Sun, "in tune with lots of working men and women in Britain. We on the Sun think that Cameron is showing a sense that he understands what people want in this country."

But Pascoe-Watson - who will lead a revamped Sun politics team that includes a new signing from the Sunday Times, Andrew Porter, as his deputy - has some encouraging words for Brown too. "Although [Brown] has a past, my reading of him is that he has been very strong on the economy, a very strong defender of the pound, he is Eurosceptic which is what we want him to be and seems to be perfectly in tune with us on the work ethic."

In the end, the final decision about which party to back at the next election will be taken "late in the day" by "Rupert Murdoch in discussion with the editor, with input from Trevor and I hope, next time round, from me too".